1. Field of the Invention
The present invention relates to durable substrates for displaying printed images (e.g., images produced by lithography, photolithography (e.g., xerographic copying), screen printing, gravure printing, offset printing, etc.), and methods for producing and using such substrates.
2. Description of Related Art
There has been a demand over the years for a durable substrate for use as a printable sheet. Whether for use with hand writing instruments, offset printing, xerographic printing processes (e.g., photocopiers, laser printers, or fax machines), screen printing, etc., there are many applications where a flexible, weatherproof material is desirable. For example, maps and other charts for outdoor use (e.g., ship charts, road and backpacking maps, schematic drawings for outdoor workers, etc.) are often exposed to extreme weather conditions and are regularly abused during use, such as by crumpling, improper folding, or being soiled with food, drink or dirt. Extreme environments have even more taxing demands, such as that encountered by charts or other documents used underwater.
A number of materials have been proposed to address some of these demands. For instance, a wide variety of coating materials have been proposed for use on conventional paper materials. Examples of such coatings are disclosed in U.S. Pat. No. 4,966,804 to Hasengawa et al., and 5,0313,621 to Kistner. While these materials may work adequately well for some applications, they all have undesirable limitations. Materials that are coated after application of the printed image are not readily amenable to a durable correction or modification after treatment. A more pressing concern is that coated paper products have only limited ability to withstand exposure to water or other weathering conditions. Breakdown under these conditions is even more pronounced when the materials are subjected to repeated folding or crumpling that may weaken or destroy the protective coating.
A number of other materials are employed that are fully weather resistant. One example of such material is described in U.S. Pat. No. 3,871,947 to Brekken. This material is a polymer film of polyethylene terephthalate, such as that used as an adhesive tape. While this material is far more weather resistant than coated paper materials, it tends to provide only a weak adhesion to most print media. As a result, most printed images will not remain on this type of material when subjected to active use or weathering. Another problem with plastic materials of this type is their expense both in production and printing. Although plastic materials are far more durable in use, they are generally incapable of reuse (i.e., permanent inks that must be used on these materials are not generally capable of removal) and these materials may present serious disposal concerns.
One common material used for applications where a permanent, weatherproof printed material is needed is spun bonded nonwoven high density polyethylene material sold under the trademark TYVEK by E. I. duPont de Nemours and Company, Inc. This material is highly tear-resistant and will withstand extensive exposure to water or other weathering conditions. As a result, images are often applied to this material where durability and weather-resistance is needed (e.g., backpacking maps and similar applications where the material may get wet or soiled). Despite improvements in durability, repeated exposure to water, and particularly the rigors of machine washing, demonstrates that the images on TYVEK maps will readily fade and the material will lose its shape. Accordingly, this material can be considered only moderately durable and not suitable for repeated exposure to extreme conditions. TYVEK material also continues to suffer from the problems of other plastic materials outlined above, such as compatibility with only certain print materials, inability to be readily cleaned and reused, and possible disposal problems following use.
Although it would be desirable to provide a print substrate that will accept and retain a wide variety of print images through severe water exposure and other extreme conditions, until the present invention no such material has been available. Of particular interest would be a print substrate that can retain images produced by a xerographic print process (e.g., from photocopiers or laser printers) through repeated exposure to water and abuse through robust use. Of even greater interest would be a material that can both successfully retain an image during use and also be readily cleaned and reused repeatedly as desired.
These and other purposes of the present invention will become evident from review of the following specification.